Wave responsive transmission control



Jan. 1, 1935. D. MITCHELL WAVE RESPONSIVE TRANSMISSION CONTROL Filed Aug. 24, 1951 ATTORNEY Patented Jan. 1, 1935 A E T OFF CE f'I'his inventionrelates to systems the transmission of energy, suchas-telephone Systems over which are transmitted the electrical waves representing speech. ,Moreparticularly, the invention relates to telephone circuits-especially fourwire circuitsin which transmission is controlled by switching devices responsive to theenergy transmitted thereover for the production of the desired overall effect, such as the voice waves.

v In, the. case of a telephone circuit, it is often desirable to maintaina normal, or non-operating, ,condition of disability, in order to prevent .singingf It thenbecomes necessary, of course, to cause theremoval of this normal disability when speech ,energy.isltransmitted, and it isaccordingly important that the removal of the dis ability be as nearlycertain as is possible. ,Fur-

thermore, in the case of a four-wire circuit, which the path normally disabled is associated with a pathfor transmission in theopposite direction (usually through a hybrid coil connection to an extending two-wire circuit), unbalance conditions may, and usually do, result in the reflection of energy transmitted over the latter path t ntothe former, with. thepossibility of the undesired'operaticn of the wave-responsive apparati e for controlling the transmission paths.

The principal object of the invention is the proper response to thevoice waves in a telephone circuit of the apparatus iorremoving the normal singing suppressing disability.

' One of the subordinate objects of the, invention is to render the above-discussed wave-responsive, apparatus responsive to all voice waves,

" weak as well as strong,.which are to be transfalse operation of the wave-responsiveapparatus:

In accomplishing the above-stated objects, the applicant provides. for removal .Ofgthe singing suppressing disability in responseto waves in .the transmitting path ofa predetermined on a greater magnitude, through Well-known means such as an amplifier-detector and a relay chain,

and, provides for an increaseof the sensitivity of i the wave-responsive means when the transmitted energy is lower than the predetermined magni- -;tude. I In addition, in the case of four-wire 'cir .to the minimum.

cuit operation, provision is made for the introduction of an increased loss in the receiving side of the circuit when the energy in the transmit ting side falls below the predetermined level,

whereby the chance of the undesired operation of the. transmitting switches by echoes is reduced 'The invention will be clearly understood when the following description of one desirable embodiment thereof is read with. reference to the accompanying drawing. 1 1., The single figure of the drawing shows dia; grammaticallya portion of a,,two-w ay system for the transmission of energysuch as the waves representingthe speech transmitted over a telephone systern. There are disclosed two two,- wire transmission paths L1 and L2 along with the applicants switching mission control. gg The transmission path L1 is adapted for transmission from left to right while the path LziS adaptediortransmission from right to left. As is indicated in the drawing, these two pathsmay be connected at the left end to a two-wire extending circuit. As is well understood in the art, this connection, is usually made through ahybrid coil, with the two-wire circuit balanced-by asuitable artificial impedance .It will be understoodfurther. that the balance between the two-wireline and the balancing impedance is never perfect and that, accordingly, waves passing to the two-wire circuit over the path L2 may be reflected, in part,

over thepathLi.

g It; will be noted that the path L1 is normally disabled atthepoint a, this disability; being under the .direct control of ;the so-called singing suppressor relay SS. Furthermore, provision is made for the disabling of the path L2 at point by the operation of a relay 8,, At the point I), in

path L1,""an amplifier-detector W is bridged across the circuit; It will be. noted that the transmission controlrelays SS andS are associated with the detector output circuitof the amplifier-detector .-W by circuit arrangements devised .byqthe applicant. v

This intermedi te apparatus includes relayssi, S2 and S3. Relays S1 andSz are polar relays.

Relayis has three windings an; M and an. Like- ,wisai'relay S2 has three windings wi, 'w2'a1'1d ws QOnd-itions. Relay S2 shouldbe slightlyxmore arrangements'for trans and sources of voltage, as will be more fully disclosed hereinafter.

It will: be noted. further that: apparatus is includediin the path 112 furnishing a1 variable2shunt impedance for the circuit. This apparatus includes the three-electrode vacuum tubes T and;

T connected substantially as disclosed in .the

1 drawing.

The inter-relation and the functions of the various elements of the applicants circuit will be clearly understood from the-followingdescription:

and discussion of the operation of the system..

When energy is transmitted. from.left to. right over the path L1, speech volume is regulated by a suitable device so that constant volumeisappliedl to point b. A portion of the energy is diverted at Connected in the detector output circuit of this device a-1'e' the -winding" of" relay S2, the middle windings w]. and w1"'serve as-bi'asing windings for these relaysgfthe right-handwindings w: and we" may-be" termed-the-"auxiliary' windings of these relays. relays- Si=and S2 arepolar relays; that the'various windingsare wound to actas is indicated by arrows=in thedra'wihg and thatthe eifect of the windihgswi and-"w1 i's to-holdi the armatures on their back contactss Whennocurrentisfiowing in 'win'd'ihgs wa and L03, relay S2is considerably less sensitive-thanarelay Si; and relay S1 is-slightlyless sensitive than relay S2.

If-the energy inthepath; L1 is at a predeter 'mined ora greater magnitude (which magnitude may be fixed by adjustmentof the amplifierdetector' W 'and by adjustment of theresistance R?1-)'-, the operation ofiamplifier-detector W' and the result'ant current' flow irrrelay S3 and the middl'e' windings ofrelays S2 and Si will cause the operation ofreIays Si S2'and Sn Theoperation of 'rel'ay-S2=pull's thearmatureof that relay to its frontcontact and 'compl'etesa circuit through battery Bk. and the windings ofa relays SS and S.

'Tlie' operation of relay SS removes-the normal singing suppressing disability from path L1 at point a, and the operation of relay S places an echo suppressor disability on path-E2-at' the point an Operati'orrofi S3: closes its contact, "but operatiorr of S1 prevents the charging: of conden'ser C and-"the increase ofi sensitivity. i

It may: be, however, thatthe subscriber connected topath'lh hascomparatively poor ability to operate relays; In suclr a; case, the" operation or amplifier=-detector will cause the operation of relay: S3 but 'wi'llf'ail to operate relays S1 and The contact of relay S3: is now. closed. while the armature efi relay: Si? remains on. its back-1 0011- tact. Battery B3 is now connected through a resistance R2; the contact and armature: of relay Sir/arid the bacls contact of relay+S1 to' the condenser (C; accordinglyg. while relay-S3 remains operated}. this: condenser is'. charged. Withpthe accumulation at the charge on. condenser C, two results; are accomplished: First. the volt-age on the: gridtof. the: tube: T1; which is normally considerably negativerbyt reason of the connectionoi battery Br, is gradually rendered less negative, andzcurrent. is permitted; to-flow: throughtheatube mitting path.

It will be remembered that these with certain operation of this relay. noted further that, as the singing suppressor in the auxiliary windings of the relays S1 and S2,.

the operation of these two relays is aided, or, in other words, these relays are rendered more sensitive and thus responsive to energy in path L1 which is belowthe original or predetermined level.

Theresult is that the relays SS and S are rendered responsive to this lower energy in the trans- Itwill be noted, however, that the increasedsensitivity is not produced unless thisis: necessary because of low speech energy, and accordingly, the singing suppressor control apparatus remains at a suitably low sensitivity until it is necessary to increase this sensitivity to insure operation of the relay SS.

'When the negative-voltage on the grids of tubes Tand T is reduced, as described above, in response to the lower energy in path L1, the impedance bridged across the receiving path L2 isreducedt and an increased loss is introduced in this'path I52. It will be understood that this increase of loss-reduces the chance of the undesired= operation of the amplifier-detector W and the relays controlled thereby, becausezof the refiection back overpatl'r L1 of energy coming in 'overpath L2, itbeing borne in'mind-that the transmissioncontrol relays are" now more sensitive than normally.

' It will be noted that a resistance R3 is connect-- ed in circuit with the condenser C. This resistanceshouldbeofsuch value that the charge on oond'enserrC will le'ak off quite gradually when the wave-responsive operation ceases.

lthasbeen stated above that relay Sz-lS slight- 1y more sensitive than relay S1. This arrangement provides a slight margin against clipping,

since sensitivity adjustment is made on speech energy which does-not quite'fail' to operate relay S2. However, afterthe sensitivity has been increased sufiiciently, relay S1 will operate on weak speech energy and thus preventfurther and unnecessary increase in sensitivity and loss in the receiving path. It may be desirable toemploy a del'ay circuit in path-L1 between points I) and a, asshown in tl'ie drawing.

It will= usually be desirable, in a system such as thatdescribed, to provide for the disabling of path L1 inresponse to energy transmitted over the "path L2; For this purpose, a portion of the. energy inpath L2 is diverted at point d to operate the amplifier-detector E and the relay S, which disables the path L1 at a point e over which energy inpath L1: must pass before operating the amplifier-detector W.

The transmission control arrangements, de-

scribed? above, are such that the sensitivity of the singing suppressing relay SS is automatically raised: when. this is necessary to insure operation of'th'e relay; but it will be noted that this sensitivity'isma-intained at the lowest value consistent It will be control becomes more sensitive, the loss in the opposite receiving path L2 is increased, with the result of the above-discussed reduction of false operation of the transmitting relays by reflected energyin the path L1. Strong voice waves: op-

erate relays-Sn szand-saandthereis normal'op eration of relays SS' and-'S, without increase of I sensitivity orincreaseofloss the path L'zErVoiCe waves which are weaker, but above the" noise level, operate relaysaj and cause an increase of sensitivity in S2 sufiicient" topermit its prompt operation; at. the same-I'time the loss in lineiLzliis increased for the purpose of avoiding operation of the relays by echoes refiected overulinewLi.

Relay S3 must operateon anywaveof'amplitude 7 above the noiseleveL Rielayszmust notbejoperated by echoes of transmission which is too Weak to operaterelay's',

1 -While the invention has been a specific 4 embodiment :for the :purpose -:of illustration, it will be understooduthat it'iis capable of embodiment in many other; and=;.widely; different 7 forms within the scope of-theappendedclaims.

What is claimed is:

t V i 1 1. In a system for the transmission of, energy,

, a transmission 'path,emeans for :normally .diss

abling said ,pathfcontrol means, adapted torre- 1 move the normal disability from said-path, means normally responsive to energyMia-predetermined or greater magnitudeiin said path forioperating said control meansyand auxiliary niefans'responsive to :energy in saidpathof less than the predetermined magnitude for rendering. said oper- "ating means responsive. to such energyt 2..In a system. forrthejtransmission of energy,

two paths adapted forutransmissio'n in opposite directions, the first path" being subject to the re- *fiection thereover of energynormallytransmitted over the second path, means for normally disabling :the first path,. means in the. =second1path for introducing a: variable loss therein; 1 control means adapted 1 to remove: the normal ,1 disability from said first path, means?normallyf'responsive magnitude, for rendering said operating means responsive to such energy,and means responsive toyenergy in said first path of less than thepres determined magnitude for increasing theloss in= troduced in saidisecondnpath ,by said variable l loss introducing means. t

3. In a system'forthe'transmission of energy,

,twotpaths' adapted for transmission in opposite directions, means for normally disabling the; first I path, control means' adapted to remove thenormal disability from 'saidrfirst path' and to disable the second path, meansinormallyresponsive'to energy of a predetermined or greater magnitude insaid first path for operating saidcontrol means, and auxiliary means responsive to energy insaidfirst' path of lesssthan the predetermined magnitude for renderingvsaid operating means V determined limits but substantially abov e the responsive tosuchenergy. e

, it 4. In a system {for the transmissiono f energy, twotpathsadapted for transmission opposite directions, the first patlibeingsubject to ,the jre- 1 fiectionthereover of, energy normally'transmitted over the second path, means for normally plac'in'g acdisability on thefirst path, means in thes'second pathlfor introducing a variable loss therein; controll means adapted toifremovesaid .idis'ability from saidfirst path and totdisablelsai'd, second path, means normally responsive to energy ro fra predetermined or greater magnitude traveling in,

said first path toward the pointpthereo niofinor-- mal disability for operating said control means,

" in said. second path;-

for renderingsa'idoperating means responsive to such i energy; means responsive to energy in said first path= of 'less than the predetermined magnitude for increasing the loss introduced in said second path by said variable loss 'introducing m n nd means responsive to energy' in said secondpath for disa'bling :said first path at a point over which energy therein must pass before affecting said operating means 1 F E 5. In a system for the transmission' of energy,

two paths adaptedfor transmission in opposite directionsfthe first path being subject to the reflection thereover of energy normally transmitted overithesecond path, means for normally disabling the first pathmeans in thesecond' path for introducing ta variable loss therein, control means adapted to. remove the normal disability from said first'path; means normally responsive to energy of -apiedetermined or greater magnitude inisaid first path for operating said control means,

auxiliary means responsive to energy in said first path of magnitude less than sufiicientto cause the operation of i said operating means 'for increasingtlie sensitivity ofsaid operating means, means responsive to energy in said first path of such lesser magnitude for increasing the loss in troducedinsaid second path by said variable loss introducing means, and means. for. preventing said increase of sensitivity and said-increase of loss while such increases are unnecessary to the operation of said disability removing means;

6. In a system for the transmission of speech energy,-including two paths adapted for transmission in opposite directions, the first path being subject tothe reflection =thereoversof energy nor-r mallytransmitted over the second pathpand means in the second path for introducing a variable loss' therein, the method oftransmission control which consists in; causing the first path to be normally disabled, causing) energy in said firstpath" of a predetermined or a greatermagnitude within certain predetermined limitsbut substantially about thelower' of said limits to remove the normal disability therefrom, and causing en ergy iinl said first path within lsaidlimits but of less than the predetermined magnitude to remove the normal disability from said first" path and to increase theloss introduced inithe second path by said variable loss introducing means. i

"7. In a systemfor the transmission of energy, including two paths adapted for xtransmissionin opposite directions, the first path beingisubject to" the reflection thereover f. energy-normally transmitted over the second path, means for normally disabling thefir'st path and means for'introducing afvariable loss in the second path, the method of transmission'control which consists in causing energy in the first path of a predetere minedior a greater magnitude within certainprelower of said'limits to remove the normal disa 'bility therefrom .and 'causing energy in said'first 8. In a system for the transmission of energy,

including ftviospaths adapted for transmission in opposite directions, the first path being subject to the reflection thereoverofi energy normally transmitted'over the second path, meansfor normally "disabling the first path, control means adapted to, remove the normal disability from said first path," means normally responsive to energy of a predeterminedaor i reater .rnagnitude said first nathiiar operating: said; control means: and gain c ntrol means for; introducing-a, rariablaloss: in

7 within said: limits but of less .thanisaidzpredetere mined. magnitude for rendering; said; :Foontrol thessecondz path-,the'method: on transmission con: trol; which. consists in. causing: energy: in said first natlrot less thanithe; predetermined;magnitude toirender; said- .operating; meanaresponsiye tasuch energy, and lcausing: energy in:- said first; pathaoi lass.thamthezprsdetenninedzmagnitudetochange the loss introducedain said; second path: by-said gaincontrollmeansi. .11

. 9; ascircuit'for; the transmission .onenergyx. the methodiof; transmission. control; which; can: sistsz'in. rendering.- .thezcirmiit disablediunder cone ditions: dined-operation; causing'ener'gy: oicraps idly fluctuating level: such. as? peech-,5 a id Sti-H': guished .from noismiinthe; circuit or; as-predetermined; or a. greater; magnitude within; certain predetermined; limitszbutsnbstantially above; the lower of saidl limits; to: produce. a; normak-operationeremoving the; hour-operative; disability; and causingrsuoh; energy im the; circuit:withinijrsaid limits but. of less;- than; the predetermined mag:- nitude..to.-produce.: an operation auxiliary :to. said normal operation for; removing: said disabilitycm responseto; the: transmission; or 311Gb! IOWEIEYBII? 110;- In asystemforthextransmission of alternating; currents, a. transmission path, meansv for normally 1 disabling: said path, .meansgzinrsaidi path ahead Of? said; disabling meansifor. regulating the volume in; said: path to bring; the amplitudes within certain: limits, controlimeansnormally responsive to energy. insaid path, at a. point-.intere mediate saidregulatingmeans;andsaiddisabling means, of' a predetermined or; greater magnitude within said." limits .but substantially. .abovathe lower of said limits;for:removing-themormal: dis. ability fromsaidcpath; andi'means responsive, to energy in said path, atrsaid. 'intermediatezpoint, withinisaid. limits but: of, less than. saidi predeten mined. magnitude for. rendering said; control means responsive to such" enerigyn.

11. In a system. for. the transmission ofralternating currents, two .paths adaptedfor'transmission) in. opposite. directions, the first. path being subject: to the reflection: thereover of ='energy.'nor-' mally transmitted oven the secondipathi means for normally disablingathe first; path-,1 means:v in the second. path. for; introducing a; variabl'ez'loss therein, means. in said first path: ahead of: said disabling. means for regulating thezvolume' in said path-t bring the amplitudes within certain limits, control means normally responsive .to energy in; said; first. path; at. a; point. intermediate said regulating means and. saidi disabling'i means",-

" of av predeterminedv or. greater. magnitudexwithin said limitsbut substantially aboye-the-lower'of' saidi limits for-l removing the; normal disability .froms'aid first path, meanszresponsivezto energy in said first. path, at said intermediate .poiht;

meansresponsive tOi'SllCh energy; and; means ree sponsive to energy in. said firstzpath' within said limits buties's than said'predeterrninedzmagnie tude for increasing the loss. introducedein' said second. path. 1 l "12: In av system for the transmission ,-of-.' alter-.

hating. currents, .t'wo pathSJadapted for; transmission in opposite directions, means forno'rmally disabling the first path, 'meanszin'said firstpath' ntermediate; saidiregulating; means and: said. dis;- ablingcmeans, on a.predetermined.or-greater:ma nitndewithin said: limitsbut substantiallyabove the, lower of: said. limits. for: removing I he; dis,-

. ability from said: firstapath and for disabling'the secQnd-rpath"; andi means resnonsive toene y' s'aidi first. path-,. at; said: intermediate: point, with.- insaidilimits but ofiless" than-said predetermined .magrfiiiude-fonwrendering; said control means; re:- sponsive tQ-such energy.

--: 13;.Ima; systemion'the transmission, of alter:- nating Currents; two; paths adapted; for transmission in opposite directions; the first. path being subject. toi the reflection. thereover; of: energy normally transmitted: over the second pat-h,. means for-normallyiplacing: adisability on;the first path means; -in-\ the second path for: introducing. a Va.-

of said disabling means for regulating. the volume injsaid pathrto. bring; the amplitudeswithin certo energyin. saidizfirst path, at a. point inter-mes diate said regulating. meansand said disabling means, of 'a'predetermined: or greater magnitude withinzsa'id: limits but substantially above the lower-of: said limits. for removing said disability from said. first path; and: forndisablingsaid sec:- ond. path,. auxiliary means. responsive to energy in said first .path,-'at: said. intermediate. point,

withirrsaid' limits but; of less.- than said predeterminediy: magnitude for rendering said control means: responsive tosuch: energy, means responsiveito. energysin; said first path. at: said. intermediate-point, within; said.limits.but-.. of less than saidgpredetermined. magnitude for increasing. the lossa-introduced; in. said, second path, and: means responsive;toenergyiin said; second. path for disabling said first' pathuat a; point over. which. energy' therein must: pass .beforelafiecting said: cone UIOII'IIIBQIHS;

- 14:. In; a system: for the transmission of. alter:-. nating; currents-two paths:adapted for transmise sionin opposite-directions; the first. path being subject. to the refiectionthereover. of: energy. normallystransmitted .over the, second: path; means for normally-disabling the firstpatlr, means, in the second path for. introducing a. variable loss riablezlosstherein; means in the first path ahead 20. tain limits; control-1.meansnormally. responsive V 0," Jul.

therein, means in said first: path'gahead. of said disabling-means for regulating; the volume .in said path-tobring the amplitudes within certain-lim its,--contr.ol: means normally responsive. to energy in said. first. path, at a,pointiiintermediate. said regulatingfmeanslandi'saidadisabling means, of a predetermined or. greater. magnitude within. said limits'r'hut substantially. above the. lower: of said limits for removing. the normal disability. from said first path,. auxiliary-means Eresponsive. toienergyin' said firstzpath, 'at'said: intermediate point, within said-limits but. ofeless than said-predetermined magnitude for increasing. the sensitivity. of said control means, means responsive to .energyinzsaid first path, at said intermediate point, of such lesserqmagnitude for increasing theloss in said-second pat-11,: and: means for; preventing said increase of sensitivity. and: said increaseof loss while. such increases: are-unnecessary to the operation of said disability removing meana l5; In a systemzfor the transmissionofialternating currents,=including two paths adapted for. transmission in. opposite directions, the method of transnfissioncontrol which consistsin causing the: first pathz'tox be normallyv disabled at. a first certain point, regulating the volume in said' first path at'a secondicertainpoint ahead. of said first point: to. bring the -amplitudes within certain yariable loss in'the second path, the method oi Q transmission oontrol which consists in regulating the volume in said first path ata second certain limits, causing energy saidfirst path at a point intermediate said first and second points whichenergy is of a predetermined or greater magnitude within said limits but substantially above the lower of said limits to remove the normal disability from said first path; and causing energy in said path at said intermediate point which energy is within said limits butofless than said predetermined magnitude to remove the normal disability from said first path and to increase the loss in said second path;

16. In a system for the transmission of alter hating currents, including two paths adapted for transmission in opposite directions the'first path being subject to the reflection thereover of en-' ergy normally transmitted over the second path,

means for normally disabling the first path at a first certain point and means for introducing a point ahead of said first point to bring the amplitudes within certain limits, causing energy in and causing energy insaid first path at said innitude to remove said disability and to adjust the loss introduced by said means in said second path.

' l l DO REN MITCHELL.

vtermediate point whichenergy is within said limits but of less than said predetermined mag- 

